United States General Accounting Office

GAO Report to the Ranking Minority Member,

House Committee on International

Relations

August 1996 MINE DETECTION

Army Detector’s Ability

to Find Low-Metal

Mines Not Clearly

Demonstrated

G O A

years

1921 - 1996

GAO/NSIAD-96-198

GAO United States

General Accounting Office

Washington, D.C. 20548

National Security and

International Affairs Division

B-272391 

August 28, 1996

The Honorable Lee H. Hamilton

Ranking Minority Member

Committee on International Relations

House of Representatives

Dear Mr. Hamilton:

The dangers posed by over 80 million landmines emplaced worldwide are

the subject of much discussion. You expressed concern over the threat of

landmines to U.S. troops as they carry out their mission in

Bosnia-Herzegovina. Landmines, especially those of low-metallic content,

have been used extensively by all warring factions in the former Republic

of Yugoslavia, and 5 to 7 million mines are estimated to be in the region.

Between April 1992 and June 1995—prior to the deployment of U.S. troops

to the former Republic—there were 174 landmine incidents involving U.N.

Peacekeeping Forces, which included 204 casualties and 20 deaths.

In response to your request, this report addresses (1) how the Army’s

AN/PSS-12 portable mine detector performed in detecting low-metallic

mines in tests conducted prior to procurement, (2) the nature of the

landmine threat in Bosnia-Herzegovina, and (3) the AN/PSS-12’s potential

effectiveness there.

Background The military services use portable or handheld metal detectors as one of

several devices to detect and clear hazards such as landmines. As we

reported last year, the detection and clearance of buried explosives like

landmines is very difficult, and no ideal solution has emerged.1

Low-metallic content landmines—generally plastic-encased explosives

with some metal parts inside—are among the most difficult mines for a

metal detector to find, especially when buried. Mines placed on or

protruding above the ground surface do not pose the same detection

problem as buried mines because it is possible that they could be detected

visually.

The typical portable metal detector uses electromagnetic induction

technologies to find metal objects at or below the ground surface. These

detectors induce a magnetic field, which in turn causes a secondary

1

Unexploded Ordnance: A Coordinated Approach to Detection and Clearance Is Needed

(GAO/NSIAD-95-197, Sept. 20, 1995).

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magnetic field to form around nearby objects that have conductive

properties such as the metal in landmines. An object’s detectability is a

function of the induced magnetic field’s strength and an object’s

conductive properties, size, shape, and position. For example, copper,

aluminum, and ordinary steel are good conductors and relatively easy to

detect. Stainless steel is harder to detect than an identical piece of

ordinary steel because it offers more resistance to the induced magnetic

field and thus produces a weaker or smaller secondary magnetic field.

Portable metal detectors operate on either the continuous wave or pulse

method of transmitting and receiving. Continuous wave detectors induce

and monitor magnetic fields continuously to sense any disruptions caused

by a conductive object’s secondary field; pulse detectors transmit and

receive in alternating cycles in search of secondary magnetic fields.

In 1962, the Army fielded the AN/PSS-11, a continuous wave portable mine

detector. The last AN/PSS-11s were purchased in 1972. In the late 1970s,

the Army began a program to improve the AN/PSS-11’s durability and

maintainability by replacing its outdated electronics. As the lead service

for the Department of Defense (DOD), the Army developed such a detector,

tested it successfully, and approved its production in 1984. However,

separate attempts to produce the detector to Army specifications—in 1985

with one manufacturer and in 1987 with another—failed due to the

manufacturers’ technical or financial problems. As the AN/PSS-11 became

increasingly more difficult to support due to the unavailability of

replacement parts, the Army was faced with a shortfall. In May 1990, the

Army decided to forgo development of a new or improved detector and

instead to purchase a commercially available detector as an interim

solution to its immediate shortfall.

After screening 12 commercially available metal detectors for sensitivity,

suitability, and availability, the Army narrowed the field to two

candidates—the AN-19/2 pulse detector made by Schiebel GmbH of

Austria and the Metex 4.125 continuous wave detector made by Foerster

Instruments, Inc. In March and July 1991, the Army awarded contracts to

the respective manufacturers for test articles, with options for future buys.

In December 1991, the Army selected the Schiebel detector to replace the

AN/PSS-11 and designated it as the AN/PSS-12 Handheld Metallic Mine

Detector. By the time the contract expired in March 1996, 18,235

AN/PSS-12s had been ordered and all but a few hundred had been

delivered. The total cost of the detectors, including support items, came to

$21.9 million. Of the total, 15,553 are for the Army, 571 for the Marine

Corps, 326 for the Air Force, 323 for the Navy, and 1,462 for foreign

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military sales. As of March 1996, the Army had sent 261 of the detectors to

Bosnia. The Air Force has also sent AN/PSS-12s to Bosnia. Until 2001,

when the Army plans to field a new portable detector it is developing for

low-metallic and nonmetallic mines, the AN/PSS-12 will remain the Army’s

primary portable mine detector.

Results in Brief The ability of the Army’s AN/PSS-12 to detect low-metallic content mines

has not been clearly demonstrated. The AN/PSS-12 performed poorly

against low-metallic targets in the operational tests leading to its 1991

procurement. It did not perform as well as either the aging AN/PSS-11 or

the Foerster detector against low-metallic targets, although none met the

Army’s 92-percent detection requirement. As a result of its decisions to

(1) remove the only target that met the definition for low-metallic content

and (2) add a large metal washer to the next lowest metallic content

target, the Army eliminated low-metallic targets from the tests and from its

evaluation of the two detector candidates. Since both candidates

performed equally well against the higher metallic targets remaining in the

tests, the Army selected the Schiebel because of its lower price. In

addition to the poor portrayal of low-metallic mines from test to test, the

Army has not sufficiently controlled other factors that can affect detector

performance, such as soil type and operator proficiency. Not controlling

these factors can impair the tests’ usefulness as a predictor of

performance in the field.

The AN/PSS-12’s testing history indicates that the detector may offer only

a limited capability in Bosnia, where the majority of buried mines are of

low-metallic content. Army officials informed us that Army units have only

used the AN/PSS-12 on a limited basis in Bosnia. They stated that (1) the

AN/PSS-12 is performing well in Bosnia, and the division engineer there

expressed no interest in enhancements to the detector; (2) several other

countries chose the AN/PSS-12 and two countries successfully used it in

the former Yugoslavia, before U.S. troops deployed there; and (3) the

aluminum in the low-metallic content mines in Bosnia enhances their

detectability by the AN/PSS-12. However, information from other sources

raises questions about the AN/PSS-12’s potential performance in Bosnia.

The Air Force recently cautioned its explosive ordnance disposal

technicians in Bosnia that the AN/PSS-12 does not have the sensitivity to

detect low-metallic mines they may encounter. Some countries that

originally procured the Schiebel detector have since switched to other

detectors. An Army after-action report on U.S. operations in Somalia states

that the detector could not find low-metallic content mines. Moreover, we

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did not find data to confirm that the aluminum found in the mines buried

in Bosnia is more detectable than the steel targets used in Army tests.

We believe that the more important factor in explaining the AN/PSS-12’s

performance in Bosnia to date has been the prudent steps taken by the

Army to minimize the threat posed by the landmines there. In addition to

receiving extensive mine-awareness training, U.S. troops have been able to

pick routes that either avoid minefields or use heavy equipment, such as

vehicles equipped with rollers, to clear paths. The resultant infrequent

reliance on the AN/PSS-12 helps explain why the shortcomings it exhibited

against low-metallic targets in testing may not have been exhibited thus far

in Bosnia.

Low-Metallic Content

Mines Are a Known

Threat

According to defense intelligence information, low-metallic content mines

have been a recognized threat for the last 14 years and are a prevalent

threat in Bosnia. Low-metallic mines have been represented in Army tests

of portable and other detection systems since 1983 and were included in

the performance specifications used for the 1991 procurement of the

AN/PSS-12. Army officials informed us that a separate technology effort

was underway before 1991 to address the low-metallic and nonmetallic

threat. The Army plans to complete this effort by fiscal year 2001.

Low-Metallic Mines Are

Prevalent in Bosnia

According to the National Ground Intelligence Center,2 mines with

minimal metal content were first fielded in the early 1950s. For years,

however, no criterion or standard existed for defining a mine as having

low-metallic content. In the early 1980s, the Center established the U.S.

M-19 mine, which contains 2.46 grams of metal, as the threshold for

low-metallic mines. By this standard, only mines containing 2.46 grams of

metal or less are considered as low-metallic threats.

According to intelligence reports, over half of the landmines in Bosnia are

buried, and about 75 percent of them are low-metallic mines. The metal

content of these mines is confined to the aluminum casing around their

chemical action fuzes. About eight different types of Yugoslav landmines

with this type of fuze have been identified. The Center reported that some

former Yugoslav mines containing no metal were known to have been

manufactured. These mines’ fuzes are wrapped in plastic and would not be

2

The National Ground Intelligence Center, located in Charlottesville, Va., is the U.S. authority for

assessing the threat posed by all foreign mines. Before October 1994, it was known as the Foreign

Science and Technology Center.

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detectable by the AN/PSS-12 or any other metal detector. However, the

mines recovered so far have all contained aluminum-clad fuzes.

Fuzes used in some of these mines contain between 0.4 and 1.5 grams of

aluminum. Depending on the type, these mines may contain from one to

three fuzes, any one of which is capable of detonating the mine. Examples

include the TMA-1 and TMA-5, which contain one fuze; the TMA-2, which

contains two fuzes; and the TMA-3 and TMA-4, which contain three fuzes.

The most difficult to detect are the PMA-1, which contains less than 0.4

grams of aluminum in its fuze, laid horizontally in the mine, and the

PMA-2, which has a vertical fuze (a more difficult position for detection)

containing 0.5 grams of aluminum. For detection purposes, the metallic

content of multiple fuzes is not additive; according to Army officials, the

fuzes are positioned far enough apart in the mine as to generally limit

detection to one fuze at a time.

Low-Metallic Mine Targets

Were Included in

Requirements for the 1991

Procurement

According to Army officials, the purpose of the 1991 procurement was to

buy a detector with performance equal to or better than the AN/PSS-11.

The detection and other performance requirements for the 1991

procurement were contained in a modified military specification

associated with the earlier attempt to develop an improved version of the

AN/PSS-11. This specification required that the detector have a greater

than 92-percent probability of detecting metallic mines and mines with

small metallic content.3

 The specification described the following targets

to be detected in three different types of soils—sand, loam, and magnetite

(an iron-based soil):

• a small steel pin, 4.5 millimeters long, to simulate the M-14 mine (detection

of this pin was desired but not required in magnetite);

• a hollow aluminum tube, 44.5 millimeters long and 6.4 millimeters in

diameter;

• a steel PMN-6 striker pin, 57 millimeters long, one-third of which was 

4.8 millimeters in diameter and the remainder 9.5 millimeters in diameter;

and

• a simulated M-16 mine.

According to the 2.46 gram standard, the M-14 pin and the aluminum tube

represented low-metallic targets. The M-16 is a metal-clad mine. The

PMN-6 striker pin falls somewhere between the M-16 and the low-metallic

3

This requirement falls between the nearly 100-percent detection required for mine clearance

operations, like those in Bosnia, and the 80-percent detection required for rapidly cutting through

minefields under combat conditions.

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targets. The designation PMN-6 refers to a British-made training mine that

is a replica of the Soviet PMN mine. Like the Soviet mine, the PMN-6

training mine has a nonmetallic case and contains several metal

components in addition to the striker pin, which collectively amount to

over 17 grams of metal. According to the National Ground Intelligence

Center, the striker pin itself would not qualify as a low-metallic target

because it contains several times the amount of metal as the M-19.

Army Program Is Aimed at

Detecting Low-Metallic

and Nonmetallic Mines

According to Army officials, the Army began developing other

technologies in the mid-1980s to detect low-metallic and nonmetallic

mines. Under a program now known as the Handheld Standoff Mine

Detection System, a detector is being developed that integrates

ground-penetrating radar, infrared, and metal detection technologies,

along with electronics that are intended to synthesize and interpret the

signals from the three sensors for the operator. The detector is now in

competitive prototype testing and is slated for a production decision in

fiscal year 2001. A gap in detection capability against low-metallic and

nonmetal mines may remain until then. Our September 1995 report on

unexploded ordnance provides additional information on these

technologies.

To provide some additional capability for U.S. forces in Bosnia, the Army

is evaluating commercially available detectors that combine technologies

such as ground-penetrating radar with electromagnetic induction methods.

These detectors do not possess all of the capabilities planned for the

detector in prototyping. According to Army officials, recent tests of such

systems demonstrated a 70-percent detection capability against

low-metallic and nonmetallic mines. The Army does not consider this

detection rate acceptable for use by troops in the field. Further testing is

planned.

AN/PSS-12 Detector

Performed Poorly

Against Low-Metallic

Mines in Operational

Testing

The Army’s Test and Experimentation Command, under the auspices of

the Operational Test and Evaluation Command, conducted two

operational tests during 1991 to assess the performance of the candidate

metal detectors in a field environment. Short of war, operational testing is

the most realistic way of assessing a system’s effectiveness and suitability

for fielding. However, the operational tests had several shortcomings that

complicate the assessment of the comparative performance of the two

detector candidates and the baseline AN/PSS-11 against low-metallic

mines. In the first test, the Schiebel detector found 3.4 percent of the

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low-metallic targets, compared with 24.2 percent for the AN/PSS-11.

Because the Foerster detector was not included in the first test and the

low-metallic targets were excluded from the second test, the Foerster was

not tested against these low-metallic targets and no comparison could be

made. The Foerster detected twice as many of the lowest metal content

targets present at the beginning of the second test, but the Army

concluded the targets were not representative of the higher metallic

content Soviet mine and ruled them invalid. As performance against higher

metallic targets was equal, price became the deciding factor in the

procurement decision.

March 1991 Operational

Testing

The first operational test of the detector candidates was conducted during

March 20-28, 1991. Prior to this test, the Army had screened 12 different

commercial detectors and had eliminated all but one because of

(1) technical, performance, or production shortcomings or (2) high prices.

Two Foerster candidates were among the detectors eliminated on the

basis of price. Thus, the Schiebel was the only detector forwarded for

operational testing with the baseline AN/PSS-11 detector.

This test included four target types: metal-clad training M-15 and M-16

mines, the M-14 pin, and the PMN-6 striker pin. Given that the hollow

aluminum tube described in the specification was not used in the test, the

M-14 pin was the only low-metallic target. The results of the test are shown

in table 1.

Table 1: Detection Results From

March 1991 Operational Test

Landmine target Detector

Percent

detected

M-15 metal-clad training mine Schiebel 99.46

AN/PSS-11 99.71

M-16 metal-clad training mine Schiebel 99.43

AN/PSS-11 99.50

PMN-6 steel striker pin Schiebel 59.64

AN/PSS-11 80.83

M-14 steel pin Schiebel 3.38

AN/PSS-11 24.15

Using the 92-percent detection requirement, the Army Test and

Experimentation Command concluded that the Schiebel was not an

effective mine detector and stated:

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It is strongly recommended that the Government not purchase this mine detector as a

replacement for the AN/PSS-11 at this time. Rather, another survey should be conducted to

identify candidate mine detectors that meet military specifications outlined in the test and

evaluation master plan. Further technical and operational testing should result in a more

suitable replacement mine detector.

In a separate evaluation of the test, the Army Test and Evaluation

Command, under the auspices of the Army Materiel Command, found that:

against mines with small metallic content (i.e., the M-14 and the PMN-6), the AN-19/2

[Schiebel] fell considerably short of the PS [performance specification]

requirement. . .Indeed, its performance during test was distinctly inferior to that of the

AN/PSS-11 under the same conditions, although the AN/PSS-11 itself did not meet the PS

requirement either.

The Test and Evaluation Command did state that the procurement

decision should not depend too heavily on the detectors’ inability to detect

low-metallic mines because such mines were just a step away from

nonmetal mines, which would render a metallic mine detector useless.

Nonetheless, the Command recommended that the Army (1) not approve

the Schiebel for fielding as the AN/PSS-12 and (2) reexamine the role of

the mine detector in the Army and confirm that the detection of mines

with small metallic content remained a valid need.

Ultimately, the Army decided to eliminate the M-14 target from further

testing because it concluded that the target’s metal content was so low

that it was essentially nonmetal. It was not replaced with another

low-metallic target. Army officials informed us that the user representative

at the time did not want to reject the Schiebel on the basis of its

performance against less lethal mines such as the M-14—considered likely

to injure, rather than kill—if it could detect more lethal mines that could

kill several individuals. This was a significant decision because the M-14

pin had been cited in the performance specification and had been used in

Army testing of portable mine detectors since 1983. Such testing included

the attempted product improvements of the AN/PSS-11 and the original

screening of the 12 commercial detector candidates.

The Army realized in 1992 that the M-14 pin contained only a portion—

0.29 grams—of the total metal in the M-14 mine. According to testing

conducted in 1996, the actual mine is more detectable than the target used.

Had the Army known this at the time of the 1991 testing, it may have been

able to substitute a more authentic low-metallic mine target.

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September-October 1991

Operational Testing

Following the filing of a bid protest, the Army decided to readmit one of

Foerster’s two original candidates to the competition and therefore it

participated in the second operational test. The second operational test

was held from September 17, 1991, to October 4, 1991. It included three

examples each of the Foerster, Schiebel, and AN/PSS-11. As in the

previous test, this test used targets designated as PMN-6s to simulate

low-metallic mines. However, the second test used PMN-6 training mine

casings, which contained the steel striker pin, a spring, and a small

washer. Shortly before the test began, representatives from the program

manager’s office and the U.S. Army Engineer School (which represented

the user) contended that the PMN-6 target did not contain as much metal

as a real Soviet PMN mine. They stated that metal would have to be added

to the PMN-6 test targets already buried to make them realistic.

However, the purpose of the target was not to replicate the Soviet mine. In

fact, the test report indicated that the purpose of the PMN-6 striker pin

was to simulate the M-19 mine. The Soviet mines that the PMN-6 was

modeled after are not low-metallic mines. The National Ground

Intelligence Center reports that no Soviet landmine contains less than 

8 grams of metal, which is more than the 2.46-gram threshold. While it

would have been reasonable to ensure that the target was a fair replica of

either the M-19 low-metallic mine or the striker pin described in the

specification, it was not reasonable to insist that the target replicate the

Soviet mine. The test team maintained that adding metal to the PMN-6

target could make its detectability climb to 100 percent; thus, there would

be no way to discriminate one detector’s performance from another’s.

Ultimately, it was agreed that a 2-inch metal washer would be added to

each PMN-6 target. This was done by inserting the washers beneath the

surface and on top of the buried targets, without digging them up. Because

the M-14 low-metallic target had already been eliminated, adding metal to

the PMN-6 was a key decision because it effectively eliminated the only

remaining target the test team considered to have a metal content low

enough to differentiate the performance of one detector from another.

The Test and Experimentation Command had planned a 1-day pilot test to

work out procedures and firm up preparations for the operational test.

The Command decided to conduct the pilot test with the PMN-6 targets in

their original condition—without the large washer. Table 2 shows the

results of the pilot test.

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Table 2: Detection of PMN-6 Mine

Targets During September 1991 Pilot

Test Detector

Percent

detected

Foerster 66.67

Schiebel 32.22

AN/PSS-11 28.89

The percentages shown above are the averages for the three detectors of

each type used. The best performance by a Foerster was 76.67 percent; by

a Schiebel, 43.33 percent; and by an AN/PSS-11, 43.33 percent. While these

results were included in the test report, they were excluded in the analysis

of operational test results for the procurement decision on the flawed

basis that the target was unrepresentative of a Soviet mine.

After the pilot test, the second operational test was conducted with the

PMN-6 targets augmented with the large metal washers. The other two

mine targets included in the test were metal-clad mines and thus had high

metal content. These were the M-8, a training version of the M-16 mine,

and the TMN-46, a training version of a Soviet antitank mine. Table 3

shows the results of the test.

Table 3: Detection Results From the

September/October 1991 Operational

Test Landmine target Detector

Percent

detected

M-8 metal-clad training mine Schiebel 99.91

Foerster 99.82

AN/PSS-11 99.64

TMN-46 metal-clad mine Schiebel 99.86

Foerster 100.00

AN/PSS-11 99.59

PMN-6 training mine, augmented with washer Schiebel 99.58

Foerster 99.09

AN/PSS-11 98.51

These results showed that against the high-metallic mine targets remaining

in the operational test, all three detectors found virtually all the mines and

passed the Army’s 92-percent detection requirement. The results also

confirmed the test team’s concern that adding metal to the PMN-6 target

could cause detection percentages to climb to 100 percent for all the

detectors.

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Army Decision to Procure

Schiebel Detector Did Not

Weigh Performance

Against Low-Metallic

Mines

The Army’s decision to procure the Schiebel was based on detection

performance against only the high metal content mines. In a December 13,

1991, memorandum, the Chairman of the Source Selection Board in charge

of selecting the best detector candidate concluded that the performance

difference between the detectors was not significant and that the

additional cost of the Foerster was not justified by any significant increase

in technical or operational benefit.

Army officials informed us that because none of the detectors, including

the AN/PSS-11, could meet the 92-percent requirement against

low-metallic mines, they were equally unable to satisfactorily detect such

mines. Therefore, the ability to detect low-metallic mines was no longer a

discriminating factor in selecting a replacement for the AN/PSS-11.

Nonetheless, in the only comparable operational test, the Foerster

detector demonstrated a significantly better ability to detect the lowest

metal mine target—the pilot test’s PMN-6 target—than the Schiebel

detector. Whether the Foerster’s better performance in the pilot test was

worth its higher price was not assessed because low-metallic mines had

already been eliminated as a factor by the time the decision was made.

Varying Test

Conditions Make

Comparison of Test

Results Difficult

Over the years, the Army has gathered performance data on portable mine

detectors from a number of sources, including technical tests, operational

tests, demonstrations, and from actual use in operations, such as in

Somalia. Regardless of how data is gathered, the performance of portable

mine detectors is affected by several factors that, if not controlled, make it

difficult to compare one test or operation with another. In the numerous

tests and demonstrations of portable mine detectors conducted since 1983,

these factors have not been held to consistent, realistic, or technically

sound standards. The factors include target type, target burial depth and

position, soil type and moisture content, and the distance between the

detector head and ground surface. Performance is also affected by the

proficiency of the operator, including such factors as maintaining the

correct height and speed of the detector head as it is swept back and forth

in the search for targets, the level of training, and the operator’s ability to

pick up audio and visual cues that can help indicate the presence of a

mine. In addition, as suggested by test results, different detectors of the

same model can vary in performance.

While tests, by their nature, are conducted under controlled conditions to

provide for valid data collection and analysis, technical and operational

tests are conducted under different circumstances and are interpreted

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differently. Technical testing is intended to determine the technical

capabilities of a detector under ideal conditions. While such testing can

eliminate detectors that do not have the ability to meet performance

requirements, it is not intended to assess performance under field

conditions. Operational testing is much more realistic than technical

testing, as it can introduce more factors that affect performance results,

most importantly, the operator-machine interface. The two operational

tests of portable mine detectors the Army conducted in 1991 are

illustrative of how difficult it is to isolate detector performance from other

factors when comparing test results. Their test conditions are compared in

table 4.

Table 4: Test Conditions During 1991

Operational Testing Condition March 1991 test Sept.-Oct. 1991 test

Location Ft. Hunter-Liggett, Calif. Ft. Leonard Wood, Mo.

Soil type Sandy loam Red clay

Temperature range 40-55 degrees Fahrenheit 55-75 degrees Fahrenheit

Detectors tested AN/PSS-11, Schiebel AN/PSS-11, Schiebel,

Foerster

Targets used M-14 pin, PMN-6 striker pin,

metal-clad M-15 and M-16

Simulated Soviet PMN mine,

metal-clad M-8 and TMN-46

Specialty of operator Varied Combat engineersa

Operator training for test 12-14 hours per operator 40 hours per operator

aCombat engineers are trained in the use of countermine equipment.

Some tests are actually demonstrations, which fall somewhere between

technical and operational testing, although they do not necessarily provide

the discipline or data to support statistically valid or independent data

analysis. Demonstrations of portable mine detectors have been conducted

in a field environment; however, the detectors have been operated by

contractor personnel or Army civilian personnel. Again, as in operational

testing, they must contend with a variety of factors that can affect detector

performance. While demonstrations do not enable conclusions to be

drawn about a detector’s ability to meet military requirements, they are a

vehicle for quickly gauging a detector’s potential performance in the field.

While the use of portable mine detectors in actual operations provides

realistic information on detection performance, the number of mines

detected are not usually recorded, and the number of mines missed,

absent maps and records, may not be known. Results can also be site

specific as to soil type, moisture content, and temperatures. Thus, these

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operations do not lend themselves to quantification of a detector’s

performance. Moreover, one mishap can prove fatal. The AN/PSS-12 was

used by U.S. forces in Somalia and by U.S. contractors in Kuwait and is

currently deployed with U.S. forces in Bosnia. An Army after-action report

from operations in Somalia states that the AN/PSS-12 could not detect

low-metallic mines, but it offers no specifics on the detection shortfalls.

Although many landmines were reportedly found by U.S. contractors in

Kuwait using the Schiebel and other metal detectors, the fact that they

were buried in sand and in patterns made them easier to find than might

be the case in other situations. These operations do not provide

information on the percentage or number and types of mines that were

found by the metal detectors, nor do they indicate what mines were not

detected.

The performance of the AN/PSS-11 in several tests conducted since 1983

illustrates how the measured performance of a detector can vary from one

test to the next. In a 1983 field test outdoors at Fort Belvoir, Virginia, the

AN/PSS-11 detected 80 percent of M-14 mine targets. In 1985 testing at the

Fort Belvoir indoor mine lane facility, prototypes of the product-improved

version of the AN/PSS-11 detected none of the M-14 targets buried in sand

and 67 percent of the M-14 targets on the surface. In a 1988 field test to

establish the AN/PSS-11’s detection capabilities as a standard for an Army

development of a vehicle-mounted detection system, the AN/PSS-11

detected 82.5 percent of buried M-19 mine targets. As stated previously,

the AN/PSS-11 detected 24.2 percent of M-14 targets, 80.8 percent of

PMN-6 striker pins, and 28.9 percent of PMN-6 targets (without the large

washer) in the 1991 operational tests. The data from these various sources

defy a definitive conclusion on the performance of a detector that has

been in the Army’s inventory for 30 years.

No Problems

Reported With the

Limited Use of the

AN/PSS-12 in Bosnia

According to the Army, U.S.troops have not experienced problems with

the AN/PSS-12 in Bosnia. Army officials have cited the successful use of

the detector by other countries and the detectability of low-metallic mines

in Bosnia as further evidence of the AN/PSS-12’s potential for performance

there. However, this information is not consistent with the Army’s 1991

test results and information from other sources. Consequently, we believe

the potential effectiveness of the AN/PSS-12 against low-metallic mines in

Bosnia is inconclusive. The steps the Army has taken to minimize the

threats posed by landmines there and the resultant infrequent reliance on

the AN/PSS-12 may help to explain why the detector’s poor performance

against low-metallic targets in testing has not been exhibited in Bosnia.

Page 13 GAO/NSIAD-96-198 Mine Detection
B-272391 

Performance of the

AN/PSS-12 in Bosnia Is

Inconclusive

While the Army does not know the percentage of each type of mine

detected by the AN/PSS-12 since deploying to Bosnia, officials said that

when the detector has been used it has worked well. As of July 1996, they

reported that no U.S. troop casualties had occurred as a result of the

detector’s having failed to detect a mine in Bosnia. Army officials noted

that several other countries purchased the Schiebel detector before the

United States, including Germany, Canada, Israel, Sweden, and the United

Kingdom. They said that Canada and Sweden successfully used the

Schiebel in the former Yugoslavia before the U.S. troops deployed there.

The Schiebel was the detector of choice by contractors that conducted

mine-clearing operations in Kuwait and by the United Nations in several of

its demining operations. According to Army officials, its division engineer

in Bosnia was not interested in any performance enhancements as the

AN/PSS-12 was performing fine.

The Army also believes that the mines found so far in Bosnia have had

enough metal content to be detectable by the AN/PSS-12. While these

mines are classified as low-metallic mines, they reportedly contain more

metal than the M-14 target used in the March 1991 operational test. More

importantly, the metal contained in the Bosnian mines is aluminum.

Because aluminum is lighter than steel, a piece of aluminum that weighs

the same as a piece of steel would be considerably larger. Thus, according

to Army officials, the aluminum in the Bosnian mines not only weighs

more than the M-14 test target—it would be physically larger as well.

Other information clouds an overall picture of the AN/PSS-12’s use in

operations. During the course of our review, we learned that Germany has

decided to replace its Schiebel detectors with a detector made by Vallon

GmbH of Germany, and the Netherlands is using a Foerster detector in

Bosnia. In 1993, the United Kingdom replaced its Schiebel detectors in

Cambodia. A State Department official assisting with the international

humanitarian demining effort in Bosnia informed us that the AN/PSS-12 is

used only in conjunction with probes (pointed rods used by hand). The

Marine Corps informed us that it prefers the technology of the AN/PSS-11

and currently uses the old detector in Guantanamo Bay, Cuba. In

April 1996, the Air Force issued a message to its explosive ordnance

technicians deployed in Bosnia to clear landmines and other explosives

from airfields, cautioning them that the AN/PSS-12 does not have the

sensitivity to detect low-metallic mines they may encounter. The Air Force

is processing an urgent contracting action to purchase another metal

detector to replace its AN/PSS-12s in Bosnia. This action is unrelated to

Page 14 GAO/NSIAD-96-198 Mine Detection
B-272391 

the Army’s near-term effort to evaluate commercial detectors that

combine technologies for potential application to Bosnia.

We attempted to verify that the aluminum found in mines in Bosnia was in

fact more detectable than the steel targets used in the 1991 testing. We

contacted several countermine, testing, and explosive ordnance

organizations within the services and none reported that they had

developed credible data on the comparative detectability of different

metals. At our request, a manufacturer of measurement and detection

equipment compared the detectability of an aluminum target

approximating a 0.4-gram aluminum fuze found in Bosnian mines with a

steel target approximating the M-14 pin used in Army’s tests. The

comparison did not show that the aluminum target was unequivocally

more detectable than the steel target. We did not attempt to assess how

the detectability of a 1- to 1.5-gram piece of aluminum found in some

mines in Bosnia would compare with the more substantial PMN-6 striker

pin used in testing.

Army Has Taken Steps to

Minimize the Threat Posed

by Landmines in Bosnia

According to information we obtained from Department of State, Defense

Intelligence Agency, and Army officials, several factors have minimized

the risks landmines pose to U.S. troops in Bosnia. These steps include the

following:

• The former warring parties, who are responsible for removing landmines,

have provided maps, when available, of mined areas so that these areas

can be avoided.

• For the most part, landmines are believed to be concentrated in known

zones of separation that formerly existed between the warring factions.

These zones are avoided when possible. However, a State Department

official said less is known about the landmine threat outside these zones.

• Because U.S. forces are not taking ground as they would in a combat

situation, they can move along established routes or roads. This gives

combat engineers the opportunity to run rollers down the routes several

times to detonate mines before any attempts are made at dismounted mine

detection. Most main routes are believed to be safe.

• Some mine survey, route clearance assurance, and site clearance work has

been contracted out.

According to the State Department, areas considered cleared by the

former warring parties must still be verified by peacekeeping forces. This

is because the warring parties (1) are responsible for clearing areas only

Page 15 GAO/NSIAD-96-198 Mine Detection
B-272391 

within the first 30 days after turning the areas over, (2) do not necessarily

have the best mine detection and clearance equipment or training, and

(3) did not prepare many maps of mined areas.

Army officials have described their approach to mined areas in Bosnia as

follows. All personnel are provided with extensive mine-awareness

training before going into the theater. Before U.S. forces move into an

area, an intelligence assessment is made. Discussions are held with the

former warring parties to determine whether the area is mined and if so,

what kinds of mines were used. At a more detailed level, some exploration

may be done by engineers using probes to find sample mines. The troops

can then verify whether the mines are consistent with the initial

assessment. Data sheets on the threat mines are available that describe the

characteristics of each mine and help make an accurate identification. If

an area cannot be accessed by rollers, the combat engineers then assess

whether the mines found can be detected with the AN/PSS-12. Army

officials said they do this by actually checking the detector against the

sample mines found in the ground. If the mines can be detected with the

AN/PSS-12, then U.S. troops can go in dismounted. If the mines are not

detectable, U.S. troops do not go in dismounted. As a last resort, probes

could be used.

Recommendation Had the 1991 operational testing properly portrayed low-metallic mines,

the Army may have had greater assurance that the detector it selected as

the AN/PSS-12 was the best choice at the time against the full range of

landmines. The limitations of this testing are perhaps more apparent now

than at the time; while the testing became focused on higher metallic

content mines, low-metallic content mines are prevalent in Bosnia.

Although testing may not be able to replicate all of the conditions

expected in actual operations, it should provide a sound assessment of

detection and other performance capabilities that can serve as a consistent

baseline for comparing results from test to test. Because the 1991 testing

did not provide such a foundation, an assessment of the AN/PSS-12’s

performance in Bosnia or any operation is perhaps more subjective than it

should be.

Accordingly, we recommend that the Secretary of Defense establish and

enforce realistic and consistent test standards for testing countermine and

mine detection systems that reflect known threat mines and the conditions

under which they are likely to be encountered. Such standards should be

Page 16 GAO/NSIAD-96-198 Mine Detection
B-272391 

applied not only to the acquisition of new systems but to the evaluation of

near-term or experimental solutions as well.

Agency Comments

and Our Evaluation

DOD concurred with our recommendation to establish realistic and

consistent test standards. It also noted that the research, development,

testing, and evaluation of countermine and mine detection systems were

being reviewed by an unexploded ordnance clearance executive

committee and steering group (see app. I).

Although DOD concurred with our recommendation, it stated that the

soldiers in Bosnia are not in danger due to the performance of the

AN/PSS-12 in the presence of low-metallic mines and disagreed with any

implication to the contrary. DOD reiterated that U.S. forces avoid mines

when possible, using devices such as rollers and probes in addition to the

AN/PSS-12 when mines are encountered, and that other countries selected

the same detector before the Army did. These points were covered in the

draft report. The information available to date supports DOD’s

characterization of the relative safety of U.S. forces operating in the

presence of landmines in Bosnia. The analytical dilemma is in reconciling

the poor performance of the AN/PSS-12 against low-metallic targets in

operational testing with its reported satisfactory performance in Bosnia

where low-metallic mines are prevalent. We believe it is the prudent steps

taken by the Army to avoid and minimize the landmine threat in

Bosnia—more so than the capability of the AN/PSS-12 or the detectability

of the low-metallic content mines there relative to the test targets—that

explains the difference between the detector’s performance in operational

testing with its experience in Bosnia.

DOD also noted that an independent technical test conducted in June 1996

within DOD shows that the AN/PSS-12 can consistently detect M-14

low-metallic mines when inert mines are used instead of targets. The data

from this test indicates that the inert M-14 mine is more detectable by the

AN/PSS-12 than the M-14 firing pin first used and later removed as a target

in the 1991 operational testing, although no detection percentages were

obtained to measure consistency. The improvement is attributed to the

fact that the inert mine contains more metal than the firing pin.

The June 1996 test does raise additional questions about the usefulness of

the information obtained in Army testing since 1983 that used the M-14

firing pin as a target. However, it does not supplant the 1991 operational

test results because it was a limited technical test and was not intended to

Page 17 GAO/NSIAD-96-198 Mine Detection
B-272391 

replicate a realistic environment. In the June 1996 test, landmines were not

buried but placed on the ground with the detectors held directly over

them. The essence of the test was to lower the detector over the mine and

record the distance at which the detection was made; no searching was

involved. By comparison, in the pilot test phase of the September-October

1991 operational test, the Schiebel detector found only 32.2 percent of the

PMN-6 targets, which contained significantly more metal than the inert

M-14 mine. The need to put the June 1996 test results into the proper

perspective underscores the value of establishing realistic and consistent

test standards.

Scope and

Methodology

To obtain information for this report, we reviewed numerous documents

relating to the test and evaluation of portable mine detectors, including

several military services’ test reports since 1983, the contract file on the

AN/PSS-12 procurement, files from previous investigations of the

AN/PSS-12 procurement conducted within DOD, the after-action report on

Somalia, threat publications prepared by the National Ground Intelligence

Center, Army, Navy, and U.S. Marine Corps evaluations, and evaluations

conducted by the Naval Explosive Ordnance Disposal Technology

Division.

We interviewed officials from the Office of the Secretary of Defense; the

Departments of State, the Army, the Navy, and the Air Force; the U.S.

Marine Corps; the Defense Intelligence Agency; the National Ground

Intelligence Center; and the Joint Naval Explosive Ordnance Disposal

Technology Division. We also interviewed current and former Army

program officials, representatives from the Army contracting office at the

Army Aviation and Troop Command, current and former Army user

representatives from the Army Engineer School, representatives from the

Army Test and Experimentation Command involved with the conduct of

both operational tests, and a representative from the Army Waterways

Experimentation Station that supplied PMN-6 mines for the second

operational test. We did not visit Bosnia-Herzegovina, but information was

obtained from Army officials in direct contact with units there and from

other sources as indicated. We also interviewed representatives from

detection equipment manufacturers and, at our request, the Canadian firm,

Geonics, Ltd., conducted a laboratory test to compare the detectability of

steel and aluminum targets.

We conducted our review from December 1995 to July 1996 in accordance

with generally accepted government auditing standards.

Page 18 GAO/NSIAD-96-198 Mine Detection
B-272391 

We are sending copies of this report to other interested congressional

committees and the Secretary of Defense. We will also make copies

available to others upon request.

Please contact me at (202) 512-5140 if you or your staff have any questions

concerning this report. Major contributors to this report were 

Paul L. Francis and James B. Dowd.

Sincerely yours,

Mark E. Gebicke, Director

Military Operations and

 Capabilities Issues

Page 19 GAO/NSIAD-96-198 Mine Detection
Appendix I 

Comments From the Department of Defense

See p. 17.

See pp. 15-17.

See pp. 17-18.

See p. 14.

Page 20 GAO/NSIAD-96-198 Mine Detection
Appendix I 

Comments From the Department of Defense

(703127) Page 21 GAO/NSIAD-96-198 Mine Detection
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